The bull trout favors the deep pools of the larger cold lakes and rivers, where it feeds on zooplankton and zoobenthos, especially chironomids.
Preserving Glacier’s Native Bull Trout (pdf)
As they grow larger, they begin to feed heavily upon other fish. Indeed, the fish was once maligned out of fear that they threatened populations of other native species more prized by anglers. In coastal Washington, some of the southernmost populations of bull trout feed heavily on salmon eggs and fry, as well as fish. Confusingly, a different species (Salvelinus malma malma), today commonly called the Dolly Varden trout, is also known as "bull trout" in Canada; there has been historic confusion between the two species, likely due to an over-lapping range, similar appearance, and an over-lapping variation in appearance among members of the two species.
Both migratory and stream-resident bull trout move in response to developmental and seasonal habitat requirements. Migratory individuals can move great distances (up to 156 miles [250 kilometers]) among lakes, rivers, and tributary streams in response to spawning, rearing, and adult habitat needs. Stream-resident bull trout migrate within tributary stream networks for spawning purposes, as well as in response to changes in seasonal habitat requirements and conditions. Open migratory corridors, both within and among tributary streams, and larger rivers and lake systems are critical for maintaining bull trout populations.
The Flathead Basin population is largely adfluvial, living out most of their adult lives in a lake environment. Young are reared in spawning tributary streams (Shepard et al. 1984). Hybrids are sterile when crossed with brook trout. Bull trout grow to lengths of 37 inches and weights as heavy as 20+ pounds.
